When fluid flows over the open end of a passage with a closed or nearly closed downstream end, amplified resonant pressure waves can form. If the amplification is extreme, damage to the passage structure can occur. Many fluid flow systems employ flush or quasi-flush inlet geometries that are susceptible to this phenomenon. By way of example, FIGS. 1 and 2 show portions of an exemplary prior art precooler intake system of a commercial aircraft. Fan air 38 flows across the precooler inlet opening 30. When the downstream end of the precooler intake ducting is closed or nearly closed (e.g., by a valve 40), resonant pressure fluctuation can occur. Another example of where this phenomenon occurs is at the various piping junctions in gas pipeline networks.
Current solutions to this problem have been flow condition specific and have not been entirely satisfactory. In some instances, fluid flow systems have been redesigned entirely in order to minimize pressure fluctuations. In other systems, holes have been drilled in the passage closed end to effectively de-tune the system aero-acoustically. It is not always possible to use these types of solutions, due to limited temperature and/or pressure margins of downstream components receiving the intake fluid.
In yet other systems, the inlet duct length is shortened and an air dam is positioned upstream of the inlet to spoil the incoming flow. These modifications appear to reduce the magnitude of the pressure fluctuations, but for some inlets, the reductions may be insufficient to reduce inlet duct stresses to acceptable levels. Additionally, the performance of downstream components will be affected adversely due to the aerodynamic losses of the dam. Thus, these changes can in some instances, reduce fluid resonance to tolerable levels, but, as with the valve holes, negatively impact the flow efficiency of the system.
Thus, a need exists for a flow control device and method useful in reducing or preferably eliminating pressure fluctuations within a closed end fluid passage. The ideal device would be lightweight, inexpensive, easy to install, and easy to maintain. The present invention is directed to fulfilling this need.